linux-kernel - 2.4.x: i386/x86_64 bitops clobberings

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Date:	Sun, 08 Oct 2006 23:42:07 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	linux-kernel@...r.kernel.org,
	Willy Tarreau <wtarreau@...a.kernel.org>
Subject: 2.4.x: i386/x86_64 bitops clobberings

Hi,

after going through debugging hell with some out-of-tree code, I
realised that this patch

http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=92934bcbf96bc9dc931c40ca5f1a57685b7b813b

makes a difference: current 2.6 works with the following code sequence
as expected (printk is executed), 2.4 fails.


#include <asm/bitops.h>
#include <linux/module.h>

unsigned long a = 1;

int module_init(void)
{
	unsigned long b = 0;
	int x;

	x = __test_and_set_bit(0, &b);
	if (__test_and_set_bit(0, &a))
		printk("x = %d\n", x);

	return -1;
}


There will likely be a way to work around my issue. Nevertheless, I
wondered if that patch was already considered for 2.4 inclusion. Or is
there no risk that in-tree code is affected?

Jan



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